In the last chapter, we saw how gunpowder stimulated interest in understanding the composition of matter. The mixture of sulfur, charcoal and saltpeter (potassium nitrate) was refined until an optimal (maximally explosive) mixture was obtained. The effectiveness of the mixture was also affected by the purity of the ingredients. The ability to refine and reproduce such mixtures was dependent on an understanding of relative mass and ratios between the different mixture components. Alchemists and early scientists understood appropriate ratios for ingredients in a mixture, but determining the ratios of elements that are required to produce a given compound was sometimes a more difficult task. In fact, a systematic understanding of relative masses present in compounds and chemical reactions has only been developed over the last 300 years. Our modern periodic table is based on this knowledge. Using our current understanding of molar mass, we can now relate the amount of a substance (numbers of atoms or molecules) to its mass.
In this chapter, we want use these ideas to explore quantitative issues in chemical reactions. Specifically, we are going to study how the relations between mass, moles, and numbers of particles can be applied to chemical reactions. This topic is referred to as stoichiometry, a term derived from the Greek words stoicheion (element) and metron (to measure). Understanding the chemical world in terms of stoichiometry allows us to describe and predict the ratios in which reactants combine to generate products in a given chemical process. An understanding of stoichiometry was an important step in developing the capacity to manipulate, create, and replicate new chemical formulations. This knowledge is required for any practical fields in which new chemical substances are created, including pharmaceuticals, diagnostic medicine, agricultural chemistry, and even cosmetics.